This invention relates in general to medical catheters. It relates, more particularly, to blood vessel catheters.
Blood vessel catheters are normally either venous catheters or arterial catheters. Venous catheters, in turn, normally come in several forms. The simplest are short peripheral catheters. Next come midline catheters, central venous catheters and port catheters. Hemodialysis catheters are one form of central venous catheters and are normally placed in the superior vena cava.
The present invention may find application in each of the aforementioned venous catheters. However, it finds particularly advantageous application in hemodialysis catheters.
Hemodialysis, as practiced today, normally employs one of two types of catheter to remove blood from the patient for processing and return processed blood to the patient. Most commonly, a catheter tube containing two lumens is used, each lumen having a semi-cylindrical configuration. This is frequently referred to as a dual lumen catheter. For long-term hemodialysis, surgically implanted vascular access devices are employed. This type of device is described in U.S. Pat. Nos. 4,898,669 and No. 4,108,174.
Flow rates possible with a conventional dual lumen catheter are, as might be expected, lower than those achievable where separate tubular lumens are used to remove blood from a vein for dialysis and then return processed blood back to the vein. Thus, two tube lumens have become more and more popular as the capacity (maximum flow rate) of hemodialysis membranes has increased.
Hemodialysis membranes are now able to process blood at over 500 ml of flow per minute. Even higher processing rates are foreseeable. However, problems occur with both the line introducing purified blood back into the vein (the venous line) and the line removing blood for purification (the arterial or intake line) at flow rates above 300 ml per minute. A high flow rate from the venous line can cause whipping or xe2x80x9cfirehosingxe2x80x9d of the tip in the vein with consequent damage to the vein lining. A corresponding high flow rate into the arterial line causes the port to be sucked into the vein wall, resulting in occlusion. It should be understood, of course, that both lines normally access the superior vena cava and the designations are used for differentiation purposes.
A flow balance between the venous and arterial lines is of obvious importance. Occlusion of the arterial line is a very common limiting factor in hemodialysis. While the venous line tends to remain clear and open, because the direction of flow forces tube ports away from the vein wall, in the arterial line this high flow tends to pull the port against the vein wall, thereby sucking the wall into the port and occluding it. Andersen et al. U.S. Pat. No. 4,594,074, Quinn U.S. Pat. No. 5,451,216, Quinn U.S. Pat. No. 5,810,787, Quinn U.S. Pat. No. 5,599,322 and Quinn U.S. Pat. No. 5,571,093 all discuss the need for improved aspiration in catheters generally.
An object of the present invention is to provide an improved blood vessel catheter.
Another object is to provide a venous catheter which substantially reduces the opportunity for occlusion to occur.
Another object is to provide an improved hemodialysis catheter which is capable of delivering processed blood to the patient at high flow rates without harmful xe2x80x9cfirehosingxe2x80x9d or whipping of the catheter tip.
A further object is to provide a hemodialysis catheter which is capable of returning processed blood to the patient at flow rates of 500 ml or greater without traumatizing the patients blood vessel.
Yet a further object is to provide a hemodialysis catheter which permits high flow rates while minimizing trauma and potential red cell damage so as to avoid clotting.
Yet another object is to provide a hemodialysis catheter which increases delivered flow rates through the catheter while reducing the force or speed of flow at a bolus end port and at a side port or ports.
Another object is to provide a hemodialysis catheter which permits high flow rates through larger side ports.
The foregoing and other objects are realized in accord with the present invention by providing a venous catheter which combines a radially extending catheter tube and a bolus tip. The bolus tip has a bullet nose and a main side port. A radially extending second side port is displaced 180xc2x0 around the tube from the main side port and a radially extending third side port is axially aligned with the main side port and 180xc2x0 displaced from the second side port. The second and third side ports are formed in either the catheter tube, immediately adjacent the bolus, or in an extended bolus passage section. The combination of bolus tip configuration and port configuration and location permits high flow rates with maximum diffusion and minimum occlusion in a venous catheter.
In a first embodiment of the invention, the catheter tube has an elongated cylindrical body, fabricated of resilient plastic. An axial passageway or lumen extends the length of the cylindrical body, from a proximal to a distal end. The cylindrical wall which defines the lumen has an axially and circumferentially spaced series of radially extending ports formed in it adjacent the distal end. Each port is elongated axially of the body so as to have a race-track shaped edge. The race-track shaped edge is, in turn, semi-circular in cross-section around its entire length.
Directly opposite each port in the body of the tube, the body wall is thickened in an oval pattern to form a longitudinally elongated bulge. The bulge forms a stiffening arch in the tube wall. The arch serves to prevent the tube from buckling at the port.
The distal end of the tube has a bolus tip. The bolus tip is a separate element. It is molded of the same resilient plastic. The tip may be glued or welded to the distal end of the tube.
The bolus tip has a tube connector section adjacent the distal end of the tube, a bullet nose section and a passage section between the tube connector section and the bullet nose section. The passage section of the bolus tip has an axial passage in it adjacent the connector section and a radial passage adjacent the nose section. The axial passage is in fluid communication with the tube lumen. The radial passage leads to a main port extending radially through the side of the bolus. The main port extends circumferentially around slightly more than 180xc2x0 of the bolus, i.e., about 190xc2x0 .
In a second embodiment of the invention, the passage section of the bolus is extended and the second and third ports are formed in the side of this passage section. This second port is displaced 180xc2x0 around the axis of the bolus from the main port in the bolus. Directly opposite the second port, the passage section wall is thickened to form a longitudinally elongated bulge. The third port is axially aligned with the main port and 180xc2x0 displaced from the second port. Directly opposite the third port, the passage section wall is thickened to form a longitudinally elongated bulge.
The bulge opposite the second port stiffens the bolus at the second port and tends to hold the main port away from the vein wall. As such, it aids in preventing occlusion of the main port and, also, protects the vein wall from abrasion by the edge of the main port.
In a conventional hemodialysis catheter, for example, substantially the full pumping force is directed axially out of the end of the catheter because of its end port orientation and the size and shape of any side ports employed. Little flow is directed through such side ports. The present invention provides second and third side ports which allow higher flow rates. This redirection of flow through second and third side ports separated from the main bolus port reduces the speed or force of flow from all three. Fluid pressure is reduced before the fluid reaches the main port. This reduction in force results in better diffusion and protects against whipping.xe2x80x9d In addition, the port configurations are smoother and have no sharp edges to damage blood cells. During inflow to the catheter, clogging and occlusion due to xe2x80x9cvein wall suckingxe2x80x9d is substantially avoided.